Numerous oil-bearing solid materials exist in nature. These include tar sands and vegetable products such as soy beans and peanuts. Other non-natural oil containing solids additionally exist, such as contaminated dirt resulting from oil spills or other environmental accidents. When these oils are successfully removed from these solid or semi-solid materials, a raw oil product is recovered which can be utilized for numerous purposes including heating, cooking and in the production of synthetic materials such as plastic or rubber.
The challenge of removing oils from either natural or unnatural sources is significant based on the economic and environmental costs associated with the accumulation and processing of these materials. To compete in a global market, the processing of these materials must be performed at a cost low enough to compete with other energy sources such as traditional oil production or coal mining. For example, in the processing of tar sands which contain oil-bearing bitumen, the oil-bearing sands must first be mined, the tar sand processed and the sand cleaned sufficiently to alleviate environmental concerns upon disposal or proper placement back into the environment.
Numerous processes have been utilized to recover oil from these various natural and non-natural occurring oil-bearing materials. One particular cold water method for separating oil from sand is shown in U.S. Pat. No. 1,567,983 where oil laden sand is passed over a plurality of washing drums which loosen the oil from the sand material. The oil, having a lower specific gravity then water, rises to the water surface for collection while the sand settles to the bottom for collection. This method is inefficient based on the amount of oil remaining in contact with the sand material and the amount of water which must be used.
In another method which utilizes hot water, the oil-bearing materials are subject to a jet of high pressure steam and introduced into a mixing vessel with hot water at a temperature near the boiling point. Low pressure steam is jetted into the mixture in the mixing vessel, which produces a froth of oil, water, and tar. As the froth accumulates above the level of the water in the tank the froth can be collected and recovered. These hot water batch processes are generally ineffective due to the high cost of heating the water and additionally requires a significant capital investment in equipment.
Other methods for removing oil from oil-bearing materials use organic solvents for extraction. These solvents include gasoline, naphtha, or other materials derived from petroleum based products. One particular process which utilizes organic solvents for extraction is disclosed in U.S. Pat. No. 4,389,300 to Mitchell. Mitchell discloses a vertical extraction zone where oil laden materials are introduced into the top of the extraction zone while liquid solvent is injected into an intermediate level of the vertical bed of materials while maintaining a substantially gaseous phase in contact with a lower portion of the bed. The liquid phase is prevented from flowing downwardly by attempting to maintain a gaseous phase at a sufficient pressure in the lower portion of the extraction zone The solids are removed from the lower portion of the bed with a screw-type auger assembly.
In U.S. Pat. No. 4,401,551, also issued to Mitchell, a process is described which again utilized a two-phase interface of gaseous and liquid solvent in a vertical bed of oil-bearing materials where the treated sand is removed with an auger assembly. The invention also utilizes recovered solvent at a temperature and pressure sufficient to maintain the solvent in a liquid phase to contact the oil-bearing bituminous sand to improve recovery. However, in both of the Mitchell patents the screw-type auger assembly allows a significant loss of solvent and the process is difficult to operate as a result of the gas in the lower portion of the chamber migrating upwards while the liquid solvent falls to the bottom of the extraction chamber.
In U.S. Pat. No. 5,281,732 issued to Frank, a batch method for extracting oils from vegetables is disclosed where an extraction chamber is filled with an oil-bearing material, the air purged from the extraction zone and a normally gaseous solvent introduced into the extraction chamber in a liquid phase. The liquid solvent is then pumped through the oil-bearing materials which extracts the oil from the oil bearing solids. The recovered oil and solvent are then transported to a separator in a liquid phase for separation and eventual recovery of the oil and solvent. Due to the batch nature of this operation, this type of process is inefficient for processing substantial volumes of oil-bearing solid materials and does not efficiently remove all of the solvent from the solid materials during processing.
Thus there is a substantial need for a method and apparatus which is efficient, cost effective, environmentally safe and can be performed in a continuous mode to process tremendous volumes of oil laden materials such as tar sands or soil from environmental clean-up sites. Furthermore, a need exists for an apparatus and method which is relatively mobile and which can be transported to a processing site at a potentially remote location.